Contents

Definition

Fog comprised of supercooled water droplets which normally deposit rime ice on contact with an object with a surface temperature of less than 0°C273.15 K 32 °F 491.67 °R. Fog is generally defined in terms of visibility being less than 1000m horizontally and freezing fog typically forms in the temperature range of -0°C273.15 K 32 °F 491.67 °R to -20°C253.15 K -4 °F 455.67 °R. Freezing fog is reported as FZFG on a METAR report.

Description

Surface contact with subzero surface temperatures notwithstanding, water droplets will continue to exist in supercooled liquid form until the temperature drops below -10°C263.15 K 14 °F 473.67 °R to -20°C253.15 K -4 °F 455.67 °R at which time the droplets are likely to freeze and become ice crystals (see Ice Fog).

Effects

Freezing Fog will leave only a thin film of frost or rime ice on an aircraft, which nevertheless needs to be removed before flight with a de-icing treatment. Aircraft should also receive an anti-ice treatment before commencing a take off if freezing fog conditions exist for the taxi and take off phases of flight in order to prevent further build up of ice.